I have a couple of Rosy Barbs who are about to get an upgrade in life quality. I have a new (used) 60l tank (currently they are in a 15l tank) and as soon as we are all set, they will get some more mates.
The 15l tank they are currently in, seems quite healthy, I just got a water testing kit, Ammonia, Nitrite and Nitrate are all good, pH is a little on the high side 7.8, but from what I read, Rosys should be kept between 6 and 8, so I think we are good.
Moving to the bigger tank which I had to very thoroughly clean, as it was not used for 2 years and everything just dried into it, including mould and spiders.....
I was thinking to add about 5l clean water into the new tank with some Aquasafe, then do a 50% water change in the small one, and pour the 50% I take out, into the new tank, to start colonising it. Monitor water quality in both, and slowly keep adding water in the new tank that had been matured in the little tank, and a little fish waste so the bacteria has something to thrive on, until I have enough to transfer the rest of the water and the fish over as well. At which point I would also add the filter sponge from the small tank into the big one for some more bacteria. I imagine it would take about a month.
Does this sound like a reasonable plan? I'm very new to this.. I was entrusted to look after one of the Rosys, but I felt so bad for her being alone, and then I read more and more and now here I am asking questions to keep them happy.
The tank water has no benefit in populating a new tank with bacteria as they don't live in the water but in the filter media.
To do a tank upgrade, do water changes on the old tank to get parameters close to those from the tap (if necessary). Fill the new tank with dechlorinated water, bring it up to temperature and then take the media out of the old filter and put it in the new filter, and switch it on. Finally, move the fish. This transfers all of the good bacteria so you have an instantly cycled tank, but it's advisable to test for ammonia and nitrite daily for a week or so in case there are any minor spikes.